Apple's Leopard version of its Mac OS X added more polish and features to the Mac desktop -- and carried with it important lessons for operating systems of the future, even for arch-rival Microsoft.

When Apple released Mac OS X 10.5, frequently referred to by its code name "Leopard," the company immediately had to deal with scattered technical problems.

Among the widest reported was the "Blue Screen of Death," where the Mac froze during the installation process on the blue startup screen. The issues led one consultant to blog "it's a dark day in Apple land when the least positive attributes of Windows start showing up in their beloved BSD-based OS."

What a difference a year makes. Apple has weathered the problems, morphed both its iMac and MacBook systems to aluminum cases with clean lines, and plans to release the sixth revision, code named "Snow Leopard," to its flagship operating system.

Next year, the company could hit a milestone that it's missed for a long time and claim at least a 10 percent share of U.S. computer shipments. The company has regularly grown its shipments in the United States, reaching a 9.1-percent share in the most recent quarter, according to data from IDC.

"We have seen Apple to get back into (nearly) double-digit market share which we have not seen for a long time," says Michael Gartenberg, VP of mobile strategies for JupiterMedia. "Even in a hard economy like we have now, that will put Apple in good stead."

Along the way, Apple—and its competitors—have learned some important lessons this year, analysts say.

1. Fix problems fast

When Leopard first hit the shelves, people reported major technical problems, including the Blue Screen of Death. Yet, most people today don't remember Leopard's rough start.

"Overall, Leopard is a pretty stable operating system at this point, but the interesting thing is that it really wasn't so when it shipped," says Michael Silver, VP of research for Gartner.

Apple's ability to quickly identify the problems and release fixes successfully turned what could have been a major black mark for Apple into a minor blemish. Microsoft has had less success dodging a problematic reputation for its flagship operating system, Windows Vista. It's not necessarily an apples-to-Apple comparison: Windows Vista is a major rewrite of Microsoft's operating system, while Apple's Leopard is a minor revision. Still, Microsoft's failure to quickly fix the problems left the company with public relations damage, Silver says.

"Certainly it was a rocky road to start with Leopard, but Apple was able to make changes much quicker, and it was able to avoid that reputation that Vista has been stuck with," Silver says.

2. Style and substance matter

Apple has actively sought out a reputation for delivering an operating system with style.

With Leopard, the company added a three-dimensional perspective to the Dock—the quick launch bar at the bottom of the desktop—and added Stacks, which fan out to allow the user to select recent files. The company also brought an iTunes-like experience to file selection by adding Cover Flow to the Finder. And, in the past year, Apple has converted its lower-priced product lines, iMacs and MacBooks, to the all-aluminum cases that had only been offered on the higher-end Pro lines.

Yet, the lesson for Apple's competitors is not just that slick sells, but that style must be integrated with better features, analysts say.

"The ultimate thing is that, if you look at the Leopard experience, it is not one thing—that the computers are made out of aluminum or the slick desktop—it is the sum total of the parts," JupiterMedia's Gartenberg says.

3. One OS to bind user community

With Leopard and the other revisions of the Mac OS X, Apple has succeeded at convincing a large proportion of its users to upgrade every 18 months to 2 years. The recurring revenue from operating system upgrades is one reason why Apple continues to see good business growth.

Microsoft has not seen a major consumer movement to upgrade the operating system since Windows XP came out in 2001. Most companies that consider upgrading to Windows Vista have needed to buy new computers on which to run Microsoft latest operating system. Many companies have foregone any change until the next upgrade, Windows 7, due out next year.

"Microsoft was able to get a lot of people to upgrade to Windows XP on an existing machine," Gartner's Silver says. "But as an operating system matures, it is hard to show people that there are enough reasons and value to upgrade."

Pushing customers to upgrade to the latest operating system gives Apple less software to worry about maintaining. With every minor release of the Mac OS X, Apple typically creates a client version and a server version. Microsoft, however, released six versions of Windows Vista: Starter, Home Basic, Home Premium, Business, Enterprise, and Ultimate.

"Microsoft had so many versions of its operating system that it was hard for the average consumer to figure out," JupiterMedia's Gartenberg says. "The simplicity of Leopard is that there is just one version."

4. Don't Let Your Rival Shape Your Brand

Marketing has also been a strong point for Apple, analysts say.

Even before the release of Leopard, Apple had no small success in making fun of the PC crowd, publishing humorous commercials claiming that Macs were easier to use, friendlier and more secure than PCs.

"Apple has been doing a lot of things right, as opposed to Microsoft, where— before the last few months—they were not doing a lot of branding," says Garner's Silver. "Until recently, Microsoft made the mistake of letting a competitor define them (in terms of brand) without any response."

5. Macs Must Mean Business

Perhaps Leopard's weakest spot is its failure to bring enough enterprise-friendly features to help Macs make inroads into business. This can make it tough to say yes to Macs in the enterprise, even when a Mac fan is working inside IT.

With more than 70 percent of enterprise applications requiring Windows, according to Silver, Apple has to do more.

"Apple doesn't' have an enterprise strategy, but they have focused on making it easy for users to bring in Macs through the back door and making them work in the enterprise," Silver says.

While Leopard may not see more enterprise functionality, Apple does plan to make the next version of the Mac OS X, "Snow Leopard," integrate more completely with Microsoft's Exchange, according to Apple.